1. Field of the Invention
The present invention relates to a method for forming a Group III nitride semiconductor by MOCVD after forming an AlN buffer layer on a patterned sapphire substrate by sputtering.
2. Background Art
Since the lattice constant of sapphire is significantly different from that of Group III nitride semiconductor in forming a Group III nitride semiconductor on the sapphire substrate by MOCVD, a buffer layer is formed between the sapphire substrate and the Group III nitride semiconductor to reduce the lattice mismatch, thereby improving the crystallinity of the Group III nitride semiconductor. Generally, the buffer layer is made of AlN or GaN grown by MOCVD at a low temperature, but a technique to form the buffer layer by sputtering is also known.
In the method for producing a Group III nitride semiconductor light-emitting device, the Group III nitride semiconductor layer is formed via the buffer layer on the patterned sapphire substrate, thereby improving the light extraction efficiency.
Japanese Patent Application Laid-Open (kokai) No. 2010-10363 discloses that after thermal treatment of a sapphire substrate having an a-plane main surface, which is patterned into a concave-convex figure by dry etching, in a hydrogen atmosphere at a temperature of 1000° C. to 1500° C., an AlN buffer layer is formed on the sapphire substrate having an a-plane main surface by sputtering, and a Group III nitride semiconductor is grown on the buffer layer by MOCVD. It is also disclosed that the thermal treatment under such conditions allows the growth of Group III nitride semiconductor having high crystallinity even on the sapphire substrate having an a-plane main surface damaged by dry etching.
However, the method disclosed in Japanese Patent Application Laid-Open (kokai) No. 2010-10363 requires thermal treatment process at a high temperature, and there was a problem of production cost. Since the atomic arrangement is different on between the a-plane and the c-plane of sapphire, the thermal treatment conditions to form a Group III nitride semiconductor having good surface flatness and crystallinity should be different. However, Japanese Patent Application Laid-Open (kokai) No. 2010-10363 discloses only the case where a sapphire substrate having an a-plane main surface is used. There is no description of thermal conditions about the case where a sapphire substrate having a c-plane main surface is used.